1. Field of Art
This invention relates to electrical connectors and in particular to an electrical connector for core reinforced cables.
2. Brief Description of the Prior Art
High tension electrical cable is commonly constructed with a steel core surrounded by twisted or braided strands of a conductor metal such as aluminum or copper. The conductor strands provide both tensile strength and the necessary electrical conductive path, and the steel core gives the cable additional tensile strength.
In connecting lengths of such cable together or in affixing cable accessories such as dead ends to such cable, a connector must serve the dual purposes of providing a joint of adequate strength and providing an adequate conductive path for electrical current. Meeting these criteria has usually required that the connector be firmly affixed to and in intimate direct contact with both the steel core and the conductor strands. In the field of ACSR (Aluminum Conductor Steel Reinforced) cable, the above criteria have been met by the use of a two-piece assembly comprising an aluminum outer sleeve and a steel inner sleeve. Typically the aluminum sleeve is placed over the free end of one of the cables to be joined and moved along the cable out of the immediate region of joinder. The free ends of both cables are stripped of conductor strands to expose a length of core. These exposed core lengths are disposed in opposite ends of a steel sleeve and the sleeve is then crimped about the contained core lengths. Finally the aluminum sleeve is moved onto the region of joinder, so that the aluminum sleeve extends over the steel sleeve and over equal lengths of cable on either side of the steel sleeve. The aluminum sleeve is then crimped against the conductor strands. Alternatively, a single cable may be joined to the steel sleeve, aluminum sleeve structure in a similar manner but with the opposite end of the joinder structure suitably connected to a cable accessory, such as a dead end.
The design of such steel and aluminum sleeve assemblies is such that a given assembly can accommodate very few cable sizes. This has resulted in a proliferation of various assembly units which a cable accessory manufacturer must make and stock in order to suit the cable sizes which his various customers utilize. Consequently, a specifically designed assembly is usually required for each of the many common ACSR sizes. Additionally, it is not unusual for a particular customer to order cable made to an uncommon or non-standard size cable for a particular application, and this cable will often require a connector assembly designed especially for that cable. This wide proliferation of sizes causes undesirable cost and inventory problems.
The method of application of such assemblies presents additional undesirable aspects to the user. At least two separate crimping operations are required to effect a joint, i.e. the steel sleeve must be crimped against the cable core or cores and then the aluminum sleeve must be crimped against the conductor strands. Since many cable connectors are applied in the field, this two-operation crimping is undesirable in terms of time and equipment. Field crews must have two sets of crimping dies, one for the inner steel sleeve and another for the outer aluminum sleeve. In addition, the initial positioning of the aluminum sleeve on the cable some distance from the free end to allow positioning and crimping of the steel sleeve may be troublesome. Steel core reinforced cable generally acquires a set from the drums on which it is initially wound after manufacture, and the cable will subsequently tend to assume this set or curvature when it is not under tension. Since the cable cannot usually be held in tension at its free end during joining or affixing operations, this curvature will make it difficult to slide the aluminum sleeve along the cable away from the free end. Finally, when such a two-sleeve assembly is used to join two core reinforced cables, the insertion of the exposed cores may occasion some difficulty. Both core lengths are inserted into a common sleeve and this requires at least one of the cables to be manipulated so as to effect insertion because the sleeve will have been positioned over the exposed core of the other cable.
Previous attempts to overcome these problems have been made. For example, U.S. Pat. No. Re. 25,698 discloses a connector which is adapted to be crimped in a single crimping operation in which the outer sleeve is crimped over the inner member and the cable. The inner member, which grips the cable core, is constructed of a frangible powdered metal which fractures upon crimping. As disclosed in the patent, this structure requires a high crimping pressure. This may be troublesome especially in repair as opposed to original installation applications wherein the necessary portability of the crimping press frequently limits the force capability of the press. U.S. Pat. No. 3,125,630 discloses a similar frangible metal ferrule, but comprising a plurality of segments with interlocking fingers. Both patent disclosures appear to contemplate fixing the ferrule in the outer tube and then inserting the exposed core into the ferrule which is fixed in the tube. This means that in joining two cables both exposed cores will have to be inserted into what is essentially a common sleeve with the attendant manipulative difficulties discussed previously. These insertion difficulties are aggravated in the case when the core is made from multiple wire strands. Unless such a core is "preformed" (treated in the manufacture of the cable in such a way as to retain its shape), the individual strands of the core will tend to unravel and splay out when the surrounding strands are stripped away to expose the core at the free end.
The prior art is lacking in a disclosure of a connector for electrical cables in which the same connector is adapted for joining a wide variety of cable sizes using relatively low levels of crimping force. There is no prior teaching of how to avoid the manipulative difficulties of inserting exposed cores of cables to be joined into a common sleeve.